If you've ever wanted to make your own shampoo there are lots of recipes out there, but the one from Instructables editor scoochmaroo only requires three ingredients: liquid Castile soap, distilled water, and a bit of a light vegetable oil such as jojoba or grapeseed.

Simply mix ¼ cup distilled water, ¼ cup Castile soap ($5 for 16oz at Amazon), and a ½ teaspoon of vegetable oil together and store in a bottle. It's not as thick as commercial shampoos but you get a lot of lather.